The present invention relates to a multi-spindle synchronization control system, connected to a plurality of magnetic disk units, for controlling spindle motors such that timings at which servo heads of the respective magnetic disk units pass through indexes coincide with each other.
In a conventional spindle motor control system for a magnetic disk apparatus, an output signal from a crystal oscillator is counted, and the count is decoded by a decoder for detecting upper and lower limits of the rotation speed of a spindle motor, thereby controlling the rotation speed of each spindle motor. In addition, phase control is performed by accelerating or decelerating the spindle motor in accordance with a phase relationship between a pulse generated at the center of a sector counter and a synchronizing signal input from an external controller so that the index pulse coincides with the synchronizing signal from the external controller (see Japanese Patent Laid-Open No. 59-218672).
In the above conventional spindle motor control system for a magnetic disk apparatus, speed control is performed for each spindle motor within the range of upper and lower limits of the rotation speed of the spindle motor, and then synchronization between the respective spindle motors is controlled. Therefore, the rotation speeds of the plurality of spindle motors differ from each other and variations in rotation speed also differ from each other because loads acting on the motors are different. Therefore, it is difficult to maintain the rotation speeds and the phases of the plurality of spindle motors coincident with each other for a long period of time.